The nature of the synergism between dietary factors and the development of atherosclerosis has not been fully defined. Our studies showed that simultaneous supplementation of 10% saturated fat rich in 12:0 and 14:0 fatty acids (coconut oil) plus 1% cholesterol to the diet produced a sharp increase of plasma cholesterol, indicating a synergic influence of both dietary constituents. This increase was especially patent in the VLDL fraction, modifying the distribution of other lipid components between the core and the surface of these particles. These changes are consistent with the atherogenic function of VLDL and its responsiveness to dietary manipulation.